UNAIDS and WHO estimate that of the 40 million people living with HIV/AIDS in the world, approximately 2.8 million are 50 years and older. In the US, an estimated 1 million people are infected with HIV, although one- third of this population is unaware of their diagnosis. While HIV infection is commonly thought to affect younger adults, there are an increasing number of patients over 50 years of age living with the condition. With the introduction of highly active antiretroviral therapy (HAART) in the mid-1990s, survival following HIV diagnosis has risen dramatically and HIV infection has evolved from an acute disease process to being managed as a chronic medical condition. Over the past two decades, significant progress has been made in understanding HIV pathogenesis and disease progression, which has allowed the identification of a multitude of drug and vaccine targets. Although currently available drug therapies have greatly increased the time from HIV infection to development of AIDS, drug resistance is an inevitable consequence that limits the duration of successful treatment. In this proposal we are targeting a step in viral life cycle that is essential for viral survival and to date there are no therapeutics against this particular pathway. HIV-1 uses Tat as its viral activator and viruses mutated in Tat are not viable. We are planning to continue our work on Tat peptide derivatives (mimetics) inhibitors that could potentially inhibit virus replication both in cell culture and our humanized animal models. From our original submission, we have successfully been able to trim the original Tat 15 aa peptide inhibitor to 5 aa and have found the new peptide to be able to bind to cdk2, and cdk9 tightly and inhibit their kinase activity both in vitro and in vivo. The new peptide and its mimetic (which was not planned in the original proposal) show promising results in inhibiting HIV-1 replication in cell lines and PBMCs through various mechanisms. In the current proposal we are completely focusing on the mimetics and not the peptides anymore. We will extend our initial observations in PBMCs to various pharmacological parameters including cytotoxicity, inhibitory concentrations, and its ability to inhibit replication of numerous viral strains including patient isolates and drug and resistant strains. The inhibition studies will be performed with the two 2 generation mimetics, F07#13 and F07#19, which will allow us to select the best possible inhibitors for a given HIV clade or stain. We will also ask about the functional consequence of SWI/SNF phosphorylation by cdk2/E in relation to HIV-1 chromatin remodeling of nucleosomes. Finally, we will examine the effect of cdk9 phosphorylation by cdk2/E in presence of chromatinized HIV-1 LTR DNA. We will use in vitro biotin DNA transcription assays that uses Tat for activated transcription with and without added cdk2/E and ask in cdk9 can get phosphorylated at any of the 175, 186, 262, 347 and 363 sites. Collectively, our new mimetic inhibitors and better definition of its targets will aid in bringing a new Tat inhibitor to the clinic.